1. Field of the Invention
The present invention relates to an apparatus for manufacturing hemmed workpieces. The apparatus manufactures two kinds of workpieces of different shapes, such as a right door and a left door of a motor vehicle, by integrating an inner member and an outer member through hemming work.
2. Description of the Related Art
Doors of a motor vehicle are manufactured in the following manner. Namely, a door inner element which is made up by combining a sash, a stiffener, a beam, or the like to a door inner panel, this door inner element being generically called an "inner member", is combined with a door outer panel which is generically called as an "outer member" to thereby obtain a subassembled door. Then, a fringe (or a peripheral edge) of the door outer panel is subjected to a hemming work (also simply called "is hemmed") to thereby integrate the door outer panel and the door inner element. Thereafter, the hemmed portions on the fringe of the door outer panel are welded.
A right door and a left door of a motor vehicle are not in the same shape but are symmetrical with each other. Therefore, the right door and the left door are ordinarily manufactured in separate manufacturing lines which are prepared exclusively for the respective doors. Since this method results in a higher equipment cost, there is known an apparatus for manufacturing the right door and the left door in a common manufacturing line (see Published Unexamined Japanese Patent Application No. 145217/1978).
This conventional apparatus has a pair of door inner element assembly stations for the right door and the left door which are disposed in parallel with each other. In each of the assembly stations a plurality of door inner element constituting parts such as a door inner panel, a sash, a stiffener, a door beam, or the like are connected to each other. On a downstream side of these door inner element assembly stations, there are disposed the following stations in a line: namely, a subassembly station common to both the right door and the left door, for subassembling the doors by combining the door outer panel and the door inner element together; a hemming station for the right door, in which a hemming apparatus adapted or suitable for the right door is disposed; and a hemming station for the left door, in which a hemming apparatus adapted or suitable for the left door is disposed. Each of the right doors and the left doors is hemmed only in the corresponding hemming station. It means that a door that does not correspond to the particular hemming station is allowed to pass therethrough without being subjected to the hemming work therein.
One cycle of hemming work is made up of the following steps: i.e., a step of feeding a door into the hemming apparatus; a step of closing hemming dies of the hemming apparatus; a step of holding the hemming dies under pressure; a step of opening the hemming dies; and a step of discharging the door out of the hemming apparatus. In case the right door and the left door are respectively manufactured in exclusively prepared manufacturing lines, a right door and a left door, i.e., a total of two doors, can be manufactured in a time (i.e., a cycle time) required for one cycle of the hemming work. However, in the above-described common manufacturing line, only one door can be manufactured in one cycle time, resulting in a poor efficiency.
In view of the above point, the present invention has an object of providing a low-cost apparatus for manufacturing hemmed workpieces in which two kinds of workpieces can be manufactured at a high efficiency.